Carla Del Ponte, the ex-chief prosecutor for war crimes in former Yugoslavia, has unleashed a storm of recrimination with allegations of a trade in human body parts in Kosovo and Albania after Nato bombed Serbia in 1999.

Del Ponte claims, based on what she describes as credible reports and witnesses, that Kosovan Albanian guerrillas transported hundreds of Serbian prisoners into northern Albania where they were killed, and their organs "harvested" and trafficked out of Tirana airport.

The Kosovan government, now headed by the former guerrilla leader Hashim Thaci, dismisses the claims as untrue, while Serbia and Russia are demanding a war crimes investigation into the allegations. Del Ponte, now a Swiss ambassador, has been ordered to keep silent by the Swiss government.

The allegations are aired in Del Ponte's just published memoirs of her eight years as chief prosecutor for the international war crimes tribunal for former Yugoslavia, based in The Hague.

The Hunt: Me and War Criminals, which is published in Italian and was launched last week, has triggered controversy and added to the tensions between Kosovo and Serbia two months after the Albanian-majority province declared independence from Serbia.

In the book, Del Ponte writes that her investigators visited a house in the remote mountainous region outside Burrel, Albania, which was allegedly being used as an impromptu clinic for the butchering of 300 young Serbs captured by the Kosovo Liberation Army and transported in lorries across the border from Kosovo to Albania.

According to witnesses - including one who said he had driven some of the organs to Tirana airport, and a team of unnamed journalists who investigated the allegations - the victims had their kidneys removed before being killed later and having other organs taken.

"Prisoners were aware of the fate that awaited them, and according to the source pleaded, terrified, to be killed immediately," Del Ponte writes.

The "house-clinic" was visited by UN officials from Kosovo and tribunal investigators. "The team was shocked by what they saw," said Chuck Sudetic, a former tribunal official who is joint author of the book. "They found gauze and vials of medicines, including a muscle relaxer used during surgery."

Witness accounts, indirectly provided to Del Ponte, indicated that some of the victims were buried near the house and at a nearby cemetery. Forensic tests in the house revealed traces of blood, but investigators were unable to establish whether it was human blood. The victims were said to include Albanians and trafficked women from Russia and eastern Europe forced to work as prostitutes.

Del Ponte has long complained that the UN authorities in Kosovo blocked her attempts to investigate war crimes by Kosovan Albanians and she says that the authorities in Albania were also unhelpful. The most senior Kosovan Albanian to be tried for war crimes in The Hague, Ramush Haradinaj, a former prime minister of Kosovo and ex-guerrilla commander, was acquitted last week, sparking bitter protests in Serbia.

According to Del Ponte, a local Albanian prosecutor, who visited the house with the UN team, told her: "No Serbs are buried here. But if they did bring Serbs over the border from Kosovo and killed them, they did a good thing."

The alleged organ harvesting is said to have been uncovered by journalists who called in the UN in Kosovo and provided information to the tribunal.

"There were credible accounts of abductions and an organ harvesting operation provided to reputable journalists who have had many years of experience in the region," said Sudetic.

The journalists refused to identify their witnesses. Other sources claim the body parts were flown to Istanbul where they were transplanted into wealthy Arab patients.

Del Ponte's account is the first time such allegations have come from such an authoritative source. But officials and analysts are surprised that she should choose to air them now, five years after her investigators went to the alleged scene of the crime. Del Ponte writes that it proved impossible at the time to pursue a full investigation of the claims.

"I am surprised at the extraordinary serious allegations," said one senior tribunal official. "These allegations have formed no part of any investigation by the prosecution at the tribunal."

Mirko Klarin, an authority on the tribunal and Balkan war crimes at the Institute for War and Peace Reporting, described Del Ponte's allegations as "irresponsible and appalling ... This is more journalistic than prosecutorial. She shouldn't put rumours in her book."

The Swiss foreign ministry barred Del Ponte, now its ambassador to Argentina, from attending her book launch and ordered her to keep quiet. Senior Swiss figures are calling for her resignation.

"All I know is that she was eager to talk about the book after its publication," said Sudetic.

According to the International Committee of the Red Cross, which mediates confidential talks between Serbia and Kosovo to try to locate and identify those who vanished in the 1998-99 war, there are still 1,967 people missing. The majority are believed to be Kosovan Albanians. The 300 Serbs said to have been transported to Burrel would constitute a large part of the missing Serbs.

While there is widespread scepticism about the veracity of the claims, Human Rights Watch said Del Ponte had supplied "sufficiently grave evidence" to warrant an investigation by the Kosovo and Albanian authorities.

"Perhaps by bringing this story out now, the witnesses will step forward," said Sudetic. "Perhaps the persons who are responsible for the abductions will worry about the law catching up with them. Any persons who may have taken part in the alleged organ harvesting will sleep a little less soundly."

Profile

The least diplomatic of the four people who have served as chief prosecutor at the war crimes tribunal in The Hague, Carla Del Ponte has specialised in going for the big villains. During her eight years there, she put Slobodan Milosevic in the dock, but was cheated of triumph by his death before a verdict. She was unable to get the other two genocide suspects, Ratko Mladic and Radovan Karadzic, before the court. As a Swiss prosecutor, before moving to The Hague, she concentrated on transnational crime, investigating the Russian oligarch Boris Berezovsky and joining the Italian magistrate Giovanni Falcone in tackling the Sicilian mafia. Falcone was killed by the mafia in 1992.